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I know with mine I could tell the plate mechanism was seized by feeling it, but sucking on the diaphragm it was clear it wasn't punctured because it was like sucking on a blocked straw, i.e. no air getting through.
Seems like the previous owner had gone 20 years without oiling the vacuum or mechanical advance mechanisms--I bet that would be common, being hidden under the points, etc.! A couple of drops of oil and some wiggling back and forth and they were perfect again

I've got a complete 4k minus any hang ons i.e. No carb, dizzy, gearbox, etc. It's also missing the sump nuts and timing cover bolts,so I'm thinking if anyone wants spares I'm happy to give them your way for free plus postage if you're not in Melbourne. Let me know if you need a head or blkc or timing cover, pulleys, etc. Also have stock intake and exhaust manifold s up for grabs. Gotta get rid of everything ready to move!

I cut a tiny bit of a beer can and wrapped it around the float side of the tube, and tapped the tube and aluminium shim into the hole with a pen and a few gentle whacks with my palm.
Eventually I might look at replacing it, but for now it's wobble-free. And it seems like weber spares don't come cheap!

Thanks for the responses guys! I ended up changing points and condenser chasing an electrical issue, and swapped the leads with a spare set I had, all to no avail.
It did end up being a fueling problem, albeit a bit of a curveball! I posted the details with pictures in the thread below, but basically the little brass tube insert in the primary auxillary venturi had slid half a cm toward the air corrector jets, and was all but blocking fuel supply to the primary throat--I could only get the car going by pumping the throttle and so shooting fuel from the accelerator pump.
Thanks again! The new 5k is running a beaut!

No, it certainly wasn't on my list of possible issues... But an easy fix!
Sure is! It's noticeably lean at the start of the primary opening, but even before I rejet it, this 5k is so much quicker than the 4!
Thanks for all the help.

Problem solved!
After taking the carb off for a cleaning, I couldn't get the primary Auxiliary venturi off! Turns out the brass insert in the venturi had slid half a cm toward the float bowl, and rotated such that the opening was facing sideways instead of down toward the throttle valve. This was all but completely blocking fuel to the primary throat.
I've attached some pictures of the before and after look at the venturi for the sake of explanation. The brass tube felt quite loose in its hole, so I shimmed it with a piece of beer can and tapped it back in with a pen, with the little fuel windows facing down.

If I do this fuel is shot out of the jets up the top and it revs just fine--it seems like the issue is that when I open the throttle enough that the primary opens, as soon as the fuel from the accelerator pump is consumed, it starts gasping and will stall if the throttle is open.
Together with the fact that the problem hasn't changed after I replaced the condenser and points this morning, has me firmly in the fueling issue camp.
I have taken the carb off to give it a thorough clean, even though I put a kit through it about 4 months ago. The main jets are not blocked, and neither are the emulsifier/air corrector bits. The primary venturi is so completely stuck that I can't lift it up, so I will keep trying to remove it and then can clear out the passages.
Cheers

The change came on so quickly I think something else must be happening, even if it is compounding the lean condition...
It's the dizzy off of the 4k, bosch points dizzy. I'll track down the part numbers and get a condenser, coil and points in at the local parts shop ASAP, and update from there!
But I would've thought from what I have read that Altezza is right that the condensor could cause the bogging, but would be all or nothing--it wouldn't recover again at higher revs. Is there some way to test a condensor? Either in the car on a bench?

Thanks a lot Altezza. I've done as you've said and cleaned out the passages twice since I cleaned the jets out--although the bowl and jets looked pretty good to start.
The fact that it bogs down exclusively in the range of the primary jet was what made me suspect a fuel issue, but the pump is working fine, float and needle and seat fine, and yes you can see fuel shooting down the throats when the throttle is opened.
There is a pretty substantial "sucking" sound when it bogs down, which sounds like the engine groping for more fuel?
I know the jetting of the carb was on the lean side having been set up for a bog stock 4k--is it possible that as the piston rings seated and the motor started pulling more fuel, the lean condition got worse and worse? Seems extreme to say the least, but I'm clutching at anything in the hope my new motor is not buggered haha!
Ideally I'd be able to borrow a compression gauge of someone and check that just to rule that out too.

Mmm I cranked a couple of litres of fuel into a bucket this morning and it looks fine... I'm wondering whether it may in fact be electrical. I'm not too sure what role the condensor and coil could play in all of this, but I might look at changing them both so I can at least rule them out.

Hi all,
I have a mystery for rollaclub's finest...
I've just dropped a freshly rebuilt 5k into my KE55, and had success for the first night of driving (about 45 km). Then I noticed a flat spot under medium acceleration. This got worse and worse, to the present, where it is undriveable--bogs down and shudders when trying to accelerate past 20 km/h in any gear, but will go ok with my foot to the floor.
I've taken the carb (Weber 32/32) apart and cleaned all the jets, adjusted the flat level and checked the needle and seat. I've also changed the ignition points and checked gap and ignition timing. Initially I suspected water in the petrol tank, but having filled a bucket from the carb inlet hose, and inspecting the fuel being pumped through, it seems completely normal and un-gunky.
I'm a little lost as to what to try next--I thought of changing the ignition coil? But I'm not totally sure what these symptoms would point to as the next step. Any help would be much appreciated!!
Cheers
Jasper

re: the water in petrol theory, I'm going to take a terry can of fuel when I visit the car and put fresh fuel in the flat bowl--if it runs well for the first few minutes and then back to stumbling and sputtering, I guess I'll have to do the annoying tank draining.

The jet sizes are listed here: http://www.rollaclub.com/wiki/index.php?title=Tech:Engine/K_Series/Carburettor
It's worth checking ignition timing, points gap, spark plug gap as well as checking for vacuum leaks, as any of these things could affect your economy!